Electricity: measuring and testing – Fault detecting in electric circuits and of electric components – Of individual circuit component or element
Reexamination Certificate
2002-01-30
2003-12-09
Le, N. (Department: 2858)
Electricity: measuring and testing
Fault detecting in electric circuits and of electric components
Of individual circuit component or element
Reexamination Certificate
active
06661249
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The invention relates to a circuit configuration with a load transistor for switching a load and with a current measuring configuration for sensing a load current through the load transistor.
FIG. 1
shows such a circuit configuration with a load transistor T
10
which is embodied as a MOS (Metal Oxide Semiconductor) transistor, and a current measuring configuration
100
which is connected to the load transistor T
10
and operates according to what is referred to as the “current-sense principle.” The drain terminal of the load transistor T
10
is connected to a first supply potential V
10
and its source terminal S is connected via a load to a second supply potential GND. The load transistor T
10
functions as a switch for driving the load, the transistor T
10
in the example is conducting if a potential, which is higher than the potential at its source terminal S by a value of a threshold voltage, is applied to its gate terminal G. A load current I
10
then flows through the transistor T
10
and the load. In the current measuring configuration operating according to the current-sense principle there is a measuring transistor T
20
which is operated at the same operating point as the load transistor T
10
. The drain terminal D of the measuring transistor T
20
is connected for this purpose to the drain terminal D of the load transistor T
10
, and the gate terminal G of the measuring transistor T
20
is connected to the gate terminal of the load transistor T
10
. In order to set the operating point of the measuring transistor T
20
there is a control amplifier or operational amplifier OPV, one of whose inputs is connected to the source terminal S of the first transistor T
10
, and the other terminal of which is connected to the source terminal S of the second transistor T
20
. An output of the control amplifier OPV controls a transistor T
30
which is connected downstream of the measuring transistor T
20
in such a way that the potentials at the source terminals S of the load transistor T
10
and of the measuring transistor T
20
correspond. The load transistor T
10
and the measuring transistor T
10
are usually implemented in a common semiconductor element or chip through the use of the same manufacturing process, the transistor area of the load transistor T
10
being considerably greater than that of the measuring transistor T
20
. The current I
20
through the measuring transistor T
20
, which is operated at the same operating point as the load transistor T
10
, is proportional to the load current I
10
, the proportionality factor corresponding to the ratio of the transistor areas. A voltage U
30
, which is proportional to the load current I
10
, can then be tapped off with respect to the second supply potential GND at a resistor R
30
which is connected downstream of the transistor T
30
and one of whose terminals is connected to the transistor T
30
and the other of whose terminals is connected to the second supply potential.
A disadvantage with the circuit configuration illustrated in
FIG. 1
with a load transistor T
10
and a current measuring configuration
100
is that the current measuring configuration
100
supplies a measuring current I
20
which is proportional to the load current I
10
only if the load transistor T
10
is in the normal operating mode. An n-type channel transistor is in the normal operating mode if its drain potential is greater than its source potential, and a p-type channel transistor is in the normal operating mode if its drain potential is smaller than its source potential. The measuring configuration does not function in what is referred to as “inverse operation” of the load transistor T
10
when the source potential in n-type channel transistors is greater than the drain potential, and the current I
10
flows counter to the direction shown in FIG.
1
. In order to bring about a corresponding measuring current through the measuring transistor T
10
counter to the direction shown in
FIG. 1
, a potential which is greater than the first supply potential V
10
, in accordance with the potential at the source terminal of the load transistor T
10
, would have to be available at the source terminal S of the measuring transistor T
20
given a sufficient current yield. The provision of such a potential given sufficient current yield to provide a measuring current in the source-drain direction of the measuring transistor T
20
is not possible on-chip, that is to say in the same semiconductor element in which the load transistor T
10
and the current measuring configuration
100
are implemented, or is only possible with considerable additional expenditure.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a circuit configuration with a load transistor and a current measuring configuration which overcomes the above-mentioned disadvantages of the heretofore-known circuit configurations of this general type and which permits current to be measured during the inverse operation of the load transistor.
With the foregoing and other objects in view there is provided, in accordance with the invention, a circuit configuration, including:
a load transistor having a control terminal, a first load path terminal to be connected to a first supply potential, and a second load path terminal to be connected a load, the load transistor having a load current flowing between the first load path terminal and the second load path terminal; and
a current measuring configuration connected to the load transistor, the current measuring configuration having an output for providing a measuring current between the output of the current measuring configuration and a second supply potential, the current measuring configuration providing the measuring current such that the measuring current and the load current have respectively opposite signs and such that the measuring current and the load current have respective absolute values at least substantially proportional to one another.
In other words, the circuit configuration according to the invention has a load transistor with a control terminal, a first load path terminal which is connected to a terminal for a first supply potential, and a second load path terminal for connecting to a load. A current measuring configuration is connected to the first transistor, the current measuring configuration has an output at which a measuring current to a second supply potential is available, the measuring current has a sign opposite to that of a load current between the first and second load path terminals of the load transistor and the absolute value of the measuring current is at least approximately proportional to the absolute value of the load current.
According to one embodiment of the invention, the current measuring configuration has a measuring transistor with a control terminal, a first load path terminal and a second load path terminal. The current measuring configuration also has a control circuit with a controllable resistor which is connected to the second load path terminal of the measuring transistor, and a drive circuit for driving the resistor, the drive circuit driving, according to one embodiment, the controllable resistor as a function of a first load path voltage between the first and second load path terminals of the load transistor, and as a function of a second load path voltage between the first and second load path terminals of the measuring transistor, in such a way that the absolute value of the second load path voltage corresponds to the absolute value of the first load path voltage, and the second load path voltage has a sign which is reversed in comparison with the first load path voltage.
According to a further embodiment of the circuit configuration according to the invention, there is provision for the drive circuit to set the absolute value of the second load path voltage to be smaller than the absolute value of the first load path voltage.
The drive circuit preferably adjusts the voltage between the control terminal and the s
Greenberg Laurence A.
Infineon - Technologies AG
Kerveros James
Le N.
Locher Ralph E.
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